The reduction-oxidation (redox) flow battery is an electrochemical storage device that stores energy in a chemical form and converts the stored chemical energy to an electrical form via spontaneous reverse redox reactions. The reaction in a flow battery is reversible, so conversely, the dispensed chemical energy may be restored by the application of an electrical current inducing the reversed redox reactions. A single redox flow battery cell generally includes a negative electrode, a membrane barrier, a positive electrode and electrolytes containing electro-active materials. Multiple cells may be combined in series or parallel to create a higher voltage or current in a flow battery.
Electrolytes are typically stored in external tanks and are pumped through both sides of the battery. When a charge current is applied, electrolytes lose electron(s) at the positive electrode and gain electron(s) at the negative electrode. The membrane barrier separates the positive electrolyte and negative electrolyte from mixing while allowing ionic conductance. When a discharge current is applied, the reverse redox reactions happen on the electrodes. The electrical potential difference across the battery is maintained by chemical redox reactions within the electrolytes and may induce a current through a conductor while the reactions are sustained. During charge, the electrolytes may be restored to their initial composition for discharge. The amount of energy stored by a redox battery is limited by the amount of electro-active material available in electrolytes for discharge, depending on the total electrolytes volume and the solubility of the electro-active materials.
Hybrid flow batteries are distinguished by the deposit of one or more of the electro-active materials as a solid layer on an electrode. Hybrid batteries may, for instance, include a chemical that forms a solid precipitate plate on a substrate at some point throughout the charge reaction and may be dissolved by the electrolyte throughout discharge. During charge, the chemical may solidify on the surface of a substrate forming a plate near the electrode surface. Regularly this solidified compound is metallic. In hybrid battery systems, the energy stored by the redox battery may be limited by the amount of metal plated during charge and may accordingly be determined by the efficiency of the plating system as well as the available volume and surface area for plating.
One example of a hybrid redox flow battery uses iron as an electrolyte for reactions wherein on the positive electrode each of two Fe2+ ions each loses an electron to form Fe3+ during charge, while each of two Fe3+ ions gains an electron to form Fe2+ during discharge. On the negative electrode, Fe2+ ions receive two electrons and deposit as iron metal during charge, while iron metal loses two electrons and re-dissolves as Fe2+ during discharge:2Fe2+Fe3++2e−  (Positive/Redox Electrode)Fe2++2e−FeO  (Negative/Plating Electrode)
However, when multiple flow cells are used in parallel, the cells must be hydraulically connected through an electrolyte circulation path. This can be problematic, because these electrolytes are electrically conductive and therefore shunt current can flow through the electrolyte circulation path cells driven by cell-to-cell voltage differences, causing energy losses and imbalances in the individual charge states of the cells.
The inventors herein have devised systems and methods to address these issues. In one example, a system for a flow cell for a flow battery, comprising: a first flow field; and a polymeric frame, comprising: a top face; a bottom face, opposite the top face; a first side; a second side, opposite the first side; a first electrolyte inlet located on the top face and the first side of the polymeric frame; a first electrolyte outlet located on the top face and the second side of the polymeric frame; a first electrolyte inlet flow path located within the polymeric frame and coupled to the first electrolyte inlet; and a first electrolyte outlet flow path located within the polymeric frame and coupled to the first electrolyte outlet. In this way, shunt currents may be minimized by increasing the length and/or reducing the cross-sectional area of the electrolyte inlet and electrolyte outlet flow paths.
In another example a system for a flow cell stack for a flow battery, comprising: two or more electrolyte inlet feeds; two or more electrolyte outlet feeds; and two or more flow cells, each flow cell comprising: a first flow field plate; a second flow field plate; and a polymeric frame, comprising: a top face; a bottom face; a first side; a second side, opposite the first side; a first electrolyte inlet located on the top face and the first side of the polymeric frame; a first electrolyte outlet located on the top face and the second side of the polymeric frame; a first electrolyte inlet flow path located within the polymeric frame and coupled to the first electrolyte inlet; a first electrolyte outlet flow path located within the polymeric frame and coupled to the first electrolyte outlet; a second electrolyte inlet located on the bottom face and the first side of the polymeric frame; a second electrolyte outlet located on the bottom face and the second side of the polymeric frame; a second electrolyte inlet flow path located within the polymeric frame and coupled to the first electrolyte inlet; and a second electrolyte outlet flow path located within the polymeric frame and coupled to the first electrolyte outlet. In this way, the electrolyte inlets and outlets may be separated for each flow cell, thereby managing voltage differences between cells, decreasing shunt current between cells, and increasing the performance of the battery.
In yet another example, a system for an all-iron hybrid flow battery, comprising: a redox electrolyte tank including a redox electrolyte; a plating electrolyte tank including a plating electrolyte; and a power module coupled to the redox electrolyte tank via a first pump and further couple to the plating electrolyte tank via a second pump, the power module comprising an internally manifolded flow cell stack. the internally manifolded flow cell stack comprising: two or more electrolyte feeds connected to the redox electrolyte tank and/or the plating electrolyte tank; a first sub-stack comprising at least a first flow cells coupled to a first electrolyte feed; and a second sub-stack comprising at least a second flow cells coupled to a second electrolyte feed. In this way, flow cells with similar voltages may be coupled together within a sub-stack, and shunting losses may be minimized by using separate inlet and outlet ports for each sub-stack.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It will be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description, which follows. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined by the claims that follow the detailed description. Further, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.